This study investigates the corrosion resistance and durability of Plasma Electrolytic Oxidation (PEO) coatings on flat and biomimetic-textured (riblet) AA2024 aluminum alloy substrates. Two silicate-based electrolytes were compared: a reference alkaline bath and a modified formulation containing 10 g/L of acetic acid designed to regulate plasma discharge kinetics. To further enhance barrier properties, a hydrothermal post-treatment sealing ZnAl-based was applied. Morphological analysis showed that the addition of acetic acid reduced the average coating thickness from 19 +/- 1 & micro;m to 14 +/- 1 & micro;m while promoting a significantly denser oxide structure. Electrochemical Impedance Spectroscopy in freshwater revealed that the sealed hybrid system achieved a low-frequency impedance modulus (|Z|0.01 Hz) of 2.9 & sdot;107 Omega & sdot;cm2 on flat substrates and 1.7 & sdot;106 Omega & sdot;cm2 on textured riblets, representing an increase of up to three orders of magnitude compared to the bare alloy (103 Omega & sdot;cm2). Potentiodynamic polarization corroborated these findings, demonstrating that the sealed systems achieve corrosion current densities two orders of magnitude lower than the untreated alloy in simulated freshwater. In aggressive simulated seawater, while the higher chloride concentration triggers a general increase in current density, the sealed coatings maintain a significant performance advantage, outperforming unsealed PEO formulations by at least one order of magnitude. Accelerated corrosion testing confirmed exceptional durability, with the hybrid coatings remaining intact after 2000 h of continuous Neutral Salt Spray exposure. Conversely, cyclic Prohesion testing triggered localized failure after approximately 500 h, highlighting the role of salt crystallization in promoting coating perforation. These results validate the hybrid PEO-LDH system as a robust protection strategy that preserves the integrity of functional surface textures for aeronautical and marine applications.

Carbon dioxide (CO2) corrosion affects the integrity of energy and process infrastructure, yet the field has lacked a quantitative description of its own structure and evolution. This study presents a scientometric analysis of CO2 corrosion research published between 2005 and 2025, based on 8671 documents retrieved from Scopus and Web of Science and processed in VOSviewer for co-authorship, co-citation, and keyword co-occurrence mapping. Annual output rose from low and irregular levels in the early period to sustained growth from approximately 2013 onward, and more than 80% of cumulative citations were recorded after 2016, indicating that the recently published literature constitutes the field’s actively cited base. Ranked by publication volume, China and the United States are the leading contributors across both databases, followed by a stable group of European and other national communities; at the institutional level, energy-focused organizations predominate, and Corrosion Science is the most frequently occurring and most strongly connected source in the co-citation network. Keyword co-occurrence mapping resolves the literature into four thematic clusters: physic-chemical context, degradation quantification, electrochemical and surface-analytical methods, and industrial application. The analysis also indicates that broad CO2-based queries retrieve substantial adjacent-field literature; corrosion-specific search terms are therefore suggested for delimiting this domain in future bibliometric studies.

Plasma electrolytic oxidation (PEO) of aluminum is a high-voltage anodizing treatment carried out in aqueous solution under plasma conditions, aimed at increasing its corrosion resistance. The objective of this work is to evaluate the influence of electrical variables on the quality of the resulting coating. The PEO process was performed on several AA6082 aluminum samples in an alkaline solution with added silicates. The treatment was executed in alternating current under potentiostatic conditions, combining voltage ramps with maintenance periods. The produced coatings were characterized using SEM microscopy, XRD analysis, and electrochemical tests, such as linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP), conducted in chloride-containing solutions. Results show a significant dependence of the oxide properties on the applied voltage input, influencing thickness, porosity level, and corrosion resistance.

The hydrogen embrittlement of a typical Oil Country Tubular Good (OCTG) steel, API 5CT T95, was investigated through electrochemical hydrogen pre-charging followed by mechanical testing. J-integral and tensile tests were performed on electrochemically pre-charged samples, with varying charging conditions to simulate different hydrogen environmental exposure. Hydrogen concentration profiles during the electrochemical hydrogen charging process and subsequent mechanical testing in air were calculated with the support of hydrogen permeation tests and Finite Elements Method (FEM) mass diffusion analysis. This approach enabled a deeper understanding of the actual impact of hydrogen on the assessed mechanical properties. The results were compared with tests performed in air and with data available in the literature and were critically analyzed and discussed. A toughness reduction of up to 60% was observed under the most severe charging conditions; however, the alloy retained good ductility with a critical stress intensity factor of 124 MPa√m, well above the minimum values required for pipelines in high-pressure hydrogen gas and sour service applications, 55 MPa√m and 30 MPa√m, respectively, as specified by current ASME Standard and EFC Guidelines. Tensile tests on pre-charged specimens exhibited certain limitations due to the rapid hydrogen desorption rate with respect to the time required to conduct proper slow strain-rate tests.

Surface texturing is crucial in various fields including electronics, energy, optics, and biology. Inspired by sharkskin microstructures, riblet surfaces have been extensively studied for their drag-reducing properties, particularly in aeronautical applications. Existing solutions for surface texturing based on shaped polymeric foils, however, often face wear issues and require frequent maintenance. To overcome these challenges, through-mask electrochemical micromachining (TMEMM) offers a promising approach. This study investigates TMEMM's applicability for mimicking sharkskin riblets on aluminum alloys, focusing on AA2024-T3. Ink-jet technology is introduced for mask deposition, enabling precise coverage and reducing waste. The masked samples undergo anodic polarization, with continuous and pulsed currents compared. The etching electrolyte composition is discussed and the addition of complexing agents is evaluated. Experimental results shed light on optimizing TMEMM parameters for fabricating complex structures on AA2024-T3, offering insights for riblets-base drag reduction in aeronautical applications. The crucial aspect for shaping the pointed geometry of the riblets lies in effectively combining etching parameters to ensure balanced removal rates across both depth and lateral directions.

Due to their barrier effect against chloride penetration, corrosion inhibitors are widely used to prevent chloride-induced corrosion in reinforced concrete structures. The mechanisms of interaction between the protective film on carbon steel and chloride ions represent a crucial aspect of the design of new inhibitors. Theoretical studies based on molecular mechanic (MM) and molecular dynamic (MD) methods have proven useful in research on the formation of passive films and their intermolecular interactions with chloride ions, both under dry and hydrated conditions, allowing for further comparison with experimental data. In this study, glutamate- and tartrate-based inhibitor films are investigated. After MM/MD simulations, chloride ions are found to be kept away from the dry protective films via electrostatic repulsion, hence remaining distant from the lepidocrocite γ-FeO(OH) surface. These coatings are able to efficiently prevent chloride adsorption and film penetration due to the presence of COO− groups, which electrostatically and dynamically repel chlorides over time. Even on hydrated coatings, when complete coverage of the solid surface occurs, these OCIs are good potential candidates for preventing chloride-induced corrosion; however, in the presence of water, the penetration of chloride ions across the protective films can occur, thus rendering them relatively less effective.

Aluminum alloy 2024 is largely used in the aeronautical and aerospace fields, thanks to its outstanding mechanical properties (such as high strength and toughness). Nonetheless, its use is affected by the poor corrosion resistance of such an alloy. This is due to the presence of Cu-rich intermetallic precipitates which on one hand, have a toughening effect, but on the other cause localized corrosion phenomena behaving as cathodic sites in an anodic Al matrix. Thus, a surface treatment is generally required to overcome this issue. Plasma electrolytic oxidation (PEO) is a surface treatment for producing protective coatings on metallic substrates. The process is based on the application of a high voltage between the metallic component to be treated and a counter electrode, both immersed in an alkaline solution, to reach the condition of plasma discharge. The discharges lead to a local increase in temperature and pressure causing complex plasma-chemical reactions and contributing to the formation of a ceramic-like coating. Such coatings are unfortunately affected by the presence of defects whose formation is due to the occurrence of aggressive plasma events during the treatment. These defects cause a reduction in the corrosion protection offered by PEO coatings since corrosive substances could infiltrate through them. Electrochemical oxidation (ECO) treatment is a surface treatment consisting of a modification of the PEO process. During ECO, the electrical energy applied to the electrochemical cell is properly modulated to minimise the occurrence of destructive plasma discharges while maintaining the high energy density of the process. To further improve the protective effect of the coatings it is possible to combine ECO process with sealing post-treatments to clog the porosity of the oxide layer. Commonly, sealing could be performed by immersion of the coated sample in a bath containing specific additives. Depending on the chemical composition of the sealing solution, various insoluble compounds could precipitate into the oxide layer’s defects, clogging them. The immersion step may be followed by a curing phase performed at high temperatures to stabilise the species precipitated within the pores. In the present work, ECO treatment is carried out with the aim of improving the corrosion resistance of AA2024. Moreover, two types of sealing treatments performed on ECO samples are compared, one organic while the other inorganic. ECO is carried out on AA2024 disks using an aluminate-based alkaline solution. A bipolar signal with a trapezoidal shape is applied. The applied voltage ranges from 200 to 700 V. The resulting ECO samples are post-processed by organic and inorganic sealing. The organic process is based on dipping the specimens in Ambersil 40+ protective lubricant (CRC Industries UK Ltd). The inorganic sealing consists of the immersion of the samples into an aluminophosphate bath; then curing is carried out at 300 °C for 2 hours. All the samples are characterized through SEM imaging and XRD analyses which highlight the different morphologies and phase compositions obtained depending on the specific sealing process. The organic sealed samples appear quite similar to the original ECO coatings, with globular structures covering the entire oxide surface and the main phase is aluminum oxide. Conversely, the surface of coatings sealed through the inorganic treatment appears mainly flat and even aluminophosphate is found. The corrosion assessment is performed through three electrochemical tests: potentiodynamic polarization (PDP), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). The testing solution is a 3.5 wt.% NaCl bath. According to the results of such analyses, both the sealing processes improve the corrosion resistance of the ECO coatings leading to a reduction in the corrosion current density even by two orders of magnitude (ECO i corr ~ 3∙10 -6 A/cm 2 , sealed-ECO i corr ~ 3∙10 -8 A/cm 2 ). Another outcome of the analyses is the significant time evolution of the corrosion protective performance of samples sealed with the organic sealant. Indeed, the polarization resistance, R p , of the system progressively decreases until reaching a stable value after 5 days of immersion in the aggressive solution. On the other hand, when inorganic coating is carried out a more stable behaviour of the coatings is observed and the R p remains almost constant for the entire duration of the tests.

Aluminum alloy AA6082 (Al-Si-Mg) is a lightweight alloy that requires thick barrier coatings to be protected from localized corrosion. Plasma Electrolytic Oxidation (PEO) coating is a common anodic surface treatment used for growing protective oxides; the main process variables of PEO are the composition of the electrolytic solution and the electrical input. This work focuses on the optimization of the electrical input by comparing different coatings produced by potentiostatic PEO at the effective potential of 350 V, applied by different combinations of voltage ramps with various slopes and maintenance times at the fixed potential. All processes lasted five minutes. The innovative character of this research work is the evaluation of the combined effect of the anodizing voltage and its different trends with time on the coating structure and morphology. The corrosion resistance of coated AA6082 is assessed in contact with chlorides, reproducing seawater. The resulting anodic coatings were compared in terms of structure, composition (thickness, XRD, SEM-EDS) and corrosion resistance (potentiodynamic polarization and electrochemical impedance spectroscopy), finding that longer maintenance at high anodizing potentials promotes localized high-energy plasma discharges, producing larger pores and thicker, but less protective coatings. Results show that the coating thickness increases with the maintenance time (maximum thickness value~17.6 μm). Shorter maintenance periods and longer voltage ramps lead to a lower surface porosity and enhanced corrosion performances of the oxide. The thinnest and least porous coating exhibits the best corrosion behavior (CR~1.1 μm/year).

AA2024, containing around 4% Cu and 1.5% Mg, has outstanding mechanical properties among the aluminum alloys, but poor corrosion resistance. Because of its substantial tensile strength, fatigue and wear resistance, it finds broad application in the aeronautical field. Its use, however, requires the application of a coating for ensuring adequate durability to the components. Plasma Electrolytic Oxidation (PEO) is a plasma-based coating process which has been object of growing interest in recent years because of its ability at producing thick and protective coatings by using simple, water-based electrolytes, thus reducing the environmental and safety risks presented by traditional anodizing processes. This is a promising technique for AA2024 coating, although it involves many different parameters, often interacting with each other. Thus, when optimizing it for this specific material, different effects should be considered, among which the main ones are the electrical input applied to the workpiece, the composition of the electrolytic solution and the presence of pre- or post-treatment.In the present review the main features of the PEO coating of AA2024 are treated. The main process parameters are discussed and a complete description of the discharge mechanism and of the coating growth is given. Then, the properties of the PEO coatings grown upon AA2024 are treated, mainly from the point of view of corrosion resistance enhancement. Finally, some insights into the upscaling of PEO for its industrial application are given.

AA2024 alloy (4 % Cu, 1.5 % Mg) is one of the most used in aeronautical applications because of its outstanding mechanical properties due to the presence of intermetallic precipitates. These, however, act as cathodes coupled to the aluminum matrix undermining the corrosion resistance. Therefore, AA2024 always needs a coating for being serviced. Plasma electrolytic oxidation (PEO) is a quite recent anodic coating technology exploiting plasma discharges in aqueous solutions for growing a protective oxide layer upon valve metals such as AA2024. At the same time, sharkskin biomimetic texturing is an emerging solution for the passive reduction of fluid dynamic drag. A pattern made of adjacent crests, if realized with proper dimensions, can reach a significant fuel saving upon vehicles both in air and in water. This study aims at optimizing a short potentiostatic PEO coating treatment for the application upon a biomimetic textured AA2024 surface, with the double aim of preserving the pattern parameters and enhancing corrosion resistance. The relation between electrolyte composition, spark features and coating properties has been studied by considering as main variables the cationic composition of the electrolyte (K+ and Na+) and its alkalinity. SEM observations and corrosion resistance tests allowed to establish that a reduced spark intensity can reduce the defectiveness of the oxide layer, at the price of a lower coating thickness. In particular, K+ substitution with Na+ cations and alkalinity reduction appeared to be effective in doing this, showing the best corrosion resistance and the most accurate texture reproduction.

Aluminium 2024 is one of the most widely used alloys in aeronautical applications. Despite its excellent mechanical properties, it shows very poor corrosion resistance, especially in marine environment. For this reason, it requires a coating, usually multi-layered, for being serviced. Sharkskin inspired surface texturing of aeronautical components can provide an effective fluid-dynamic drag reduction, but, since it is usually done by applying polymeric adhesives, texture durability is a common issue. Directly reproducing textures on metals offers a promising alternative. The aim of this research is thus twofold: i) to reduce the fluid-dynamic drag with a surface texture inspired by the scales (the so-called “riblets”) of the mako shark skin; ii) to improve the corrosion resistance by growing a plasma electrolytic oxidation (PEO) coating upon it, thus also extending the lifetime of the texture itself. In the first part of the work, the proper bio-inspired surface texture is discussed for different applicative scenarios: a civil use unmanned aerial vehicle (UAV), an airplane for commercial transport and a competition sailboat. In the considered one (the civil use UAV), an array of 200 µm spaced crests with a 100 µm height provides the optimum drag reduction. This texture is obtained by means of through-mask electrochemical micromachining (TMEMM). In this process, a dielectric mask is applied on the aluminium surface by ink-jet printing and UV curing, then the metal is dissolved selectively by anodic polarization in 1.17 M NaNO 3 , thus obtaining the desired texture. Different process variables have been considered and studied, among which the printed mask thickness, the presence of surface pre-treatments and the use of cation chelating agents in the solution. Microscopical observations allow to select the best process parameters for achieving an accurate texture reproduction. In parallel, the PEO coating process is optimized on textured and non-textured AA2024 specimens. Once the electrical process is established, the PEO electrolyte composition is varied for studying the effect of additives such as sodium silicate, sodium hydroxide and acetic acid. The effect of the electrolyte alkalinity is studied too. PEO coatings are characterized by microstructural analyses and electrochemical methods, among which electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves have been used for assessing the corrosion protection obtained. Finally, the application of an hydrothermal pore sealing post-treatment of 15 min in a 0.05 M Zn(NO 3 ) 2 has been considered for maximizing corrosion protection. Finally, the corrosion resistance of biomimetic textured and PEO treated surfaces has been investigated by means of multiple techniques, including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, linear polarization resistance, and potentiostatic polarization. To complement these, accelerated aging tests, such as neutral salt spray and cyclic prohesion test, were performed to assess the long-term performance of the coatings in simulated corrosive environments. The focus is on comparing the corrosion behavior of PEO-treated metal versus bare metal and assessing the potential influence of the texturing geometry on susceptibility to phenomena such as pitting nucleation. This study highlights the role of surface texturing in enhancing system durability, offering insights into its interplay with long-term protective performance. The combination of advanced PEO treatments and biomimetic designs demonstrates significant potential for improving the functional and protective properties of AA2024 aluminum alloy in demanding applications. The results presented in this work are part of the research project “MAKO - biomimetic corrosion resistant aluminium for aeronautics”, funded by European Union – Next Generation EU, PNRR - Missione 4 “Istruzione e Ricerca” - Componente C2 Investimento 1.1 “Fondo per il Programma Nazionale di Ricerca e Progetti di Rilevante Interesse Nazionale (PRIN)” D.D. n. 104/2022 “Bando PRIN 2022”.

Graphite electrodes in acidic electrolytes suffer significant degradation due to anion interactions near the oxygen evolution potential (OEP), leading to the dissolution of the graphite basal plane. 5,10,15,20-Tetraphenyl21H,23H-porphine (H2TPP) films can protect highly oriented pyrolytic graphite (HOPG) surfaces, as shown by in-situ AFM and electrochemical analysis. Though ultrathin porphyrin films are ineffective due to imperfections on the surface, thicker films, around 25 nm, form nanocrystals which initially protect but degrade over time in acidic environments, acting as a sacrificial layer (i.e., a temporary film allowed to protect a sample and removed after serving its purpose). To enhance protection, we add a fullerene (C60) layer on the H2TPP film, leveraging noncovalent interactions to shield the porphyrin from acid attack. Although fullerenes dissolve in highly concentrated sulfuric acid, they are not affected in diluted H2SO4 electrolytes at potentials where HOPG degrades. Our findings reveal that C60/H2TPP/HOPG electrodes in 1 M H2SO4 exhibit superior protective performance compared to H2TPP/HOPG alone, suggesting that the C60 layer significantly enhances the durability of the porphyrin film, offering a more robust solution for preserving the graphite electrodes under acidic conditions.

The present paper discusses the influence of oxysalts, namely tungstate, zirconate, and silicate, on the plasma evolution during the PEO process on titanium, performed in a sodium hydroxide solution. The morphology, thickness, and corrosion resistance strongly depend on the specific type of oxysalts added to the electrolytic bath. Scanning electron microscope (SEM) imaging reveals that zirconate promotes the production of thicker coatings than tungstate, while when silicate is used more porous oxides with a very rough morphology are obtained. Coatings processed with silicate also show a high level of amorphism, while the other types of oxides are mainly crystalline, as highlighted by X-ray diffraction (XRD) testing. The anti-corrosive performance is evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analyses performed in a hot sulfuric acid solution. All the PEO samples display higher polarization resistances and lower corrosion current densities than the bare titanium showing an improved corrosion resistance.

Carbon steel structures employed to convey hydrocarbons and other dangerous fluids, such as oil or flammable liquids, are equipped with degradation prevention systems, which typically consist of a cathodic protection (CP) system combined with an external insulating coating, both designed to reduce the corrosion rate below 10 µm/year. The presence of electrical interference, both AC and DC, can cause significant corrosion damage to metallic structures, even when CP is applied. DC interference is determined by the presence of a third-party CP system or public transportation system. AC interference may occur through conduction or induction mechanisms, caused by high-voltage powerlines or high-speed trains, powered by AC. Both interferences may lead to localized corrosion at coating defects, despite compliance with the −0.850 V saturated Cu/CuSO4 reference electrode (CSE) protection criterion. Considering AC-induced corrosion, both field failures and laboratory investigations have demonstrated that corrosion can occur at industrial frequencies, and when CP is applied following the standards. Even though AC-induced degradation is generally not as severe as DC interference, uncertainties remain regarding the protection potential range necessary to achieve acceptable corrosion prevention under AC interference. To formulate a CP criterion under AC interference, weight loss measurements were conducted on carbon steel samples under cathodic protection in solutions that simulate real soil conditions. Carbon steel coupons protected by CP were interfered with AC densities ranging from 1 A/m2 to 800 A/m2 for four months. During this time interval, polarization potential, protection current density and AC density were monitored. Based on the experimental data gathered during this study, a proposal for a risk map is also suggested. The results indicate that overprotection (potentials < −1.2 V CSE) represents the most dangerous scenario when AC interference is involved.

As the transport of gaseous hydrogen and its use as a low carbon-footprint energy vector become increasingly likely scenarios, both the scientific literature and technical standards addressing the compatibility of pipeline steels with high-pressure hydrogen environments are rapidly expanding. This work presents a detailed review of the most relevant hydrogen embrittlement testing methodologies proposed in standards and the academic literature. The focus is placed on testing approaches that support design-oriented assessments, rather than simple alloy qualification for hydrogen service. Particular attention is given to tensile tests (conducted on smooth and notched specimens), as well as to J-integral and fatigue tests performed following the fracture mechanics’ approach. The influences of hydrogen partial pressure and deformation rate are critically examined, as these parameters are essential for ensuring meaningful comparisons across different studies.

Metallic surface texturing is a key technique across a wide range of fields, including electronics, energy conversion, and fluid dynamics. Drawing inspiration from biological structures like the riblets on shark skin, known for their ability to reduce fluid drag by minimizing vortex formation, engineered textured surfaces have attracted significant attention. Despite this interest, conventional fabrication methods, such as polymeric coatings and additive manufacturing, often face limitations in durability due to mechanical degradation, resulting in high maintenance demands and reduced long-term efficiency. In this study, Through-Mask Electrochemical Micromachining (TMEMM) as a low-damage technique for fabricating microstructures on aluminum alloys, specifically AA1050, AA5005-H24, and AA2024-T3, was explored. TMEMM involves the ink-jet deposition of an insulating mask, followed by anodic polarization to etch precise microfeatures in the exposed metallic areas. Scanning electron microscopy reveals the dynamic evolution of geometric parameters during the etching process, providing critical insights into its progression. Potentiodynamic polarization evaluations further clarify the electrochemical behavior of the alloys post and during etching, showing how intermetallic particles and surface texture influence corrosion resistance and reactivity. This study underscores TMEMM's potential in enhancing surface functionalities while addressing alloy-specific challenges, offering insights for advancing textured surfaces in various technological domains.

Acidic corrosion in industrial environments represents a serious threat that requires an active prevention and management strategy. In this context, weak acids can create a severe corrosion environment for metallic surfaces, sometimes exceeding the severity observed in strongly acidic solutions under similar conditions. While most of the research efforts of the last decades in the field of the predictive modeling of acidic corrosion have been focused on the specific case of sweet corrosion caused by carbonic acid, the goal of this work is to describe and validate a predictive model to be used as a more transversal tool for acidic corrosion. The model, called the Tafel–Piontelli model, leverages Tafel law to mechanistically describe the electrochemical behavior of carbon steel in acidic aqueous environments. Two different acids, acetic and valeric, were used to experimentally evaluate the performance of the model in weakly acidic solutions, varying the pH and the temperature conditions. Potentiodynamic polarization tests and mass loss tests were performed, allowing us to assess the kinetic parameters (the Tafel slope and the exchange current density of the cathodic and anodic reactions) and corrosion rates of the corrosion process. The promising results suggest that the Tafel–Piontelli model is able to adapt to different scenarios and its intrinsically theoretical nature allows us to extend its predictions outside the range of experimental conditions used to validate it.

The present study investigates the influence of organic acids, added to the electrolytic solution, on the structure, morphology, and corrosion behaviour of plasma electrolytic oxidation (PEO) coatings produced on titanium grade 2. Particular attention is paid to the role of functional groups in the modification of the oxide’s properties. For this reason, all three selected acids, namely glutaric, glutamic, and tartaric acid, display two carboxylic groups, thus they interact with the substrate material mainly through –COO− adsorption. However, glutamic acid also has an amine group, while tartaric acid has two hydroxyl groups. The presence of such additional functional groups is found to impact the formation of the PEO coatings. According to scanning electron microscopy (SEM) analyses, the number of defects and their dimension increase with an increasing number of active groups present in the organic molecules. Then, when glutaric acid with only two carboxyl groups, is employed as an additive, smaller pores are produced. The dimension of defects increases when glutamic and tartaric acid are used. X-ray diffraction (XRD) testing demonstrates that rutile and anatase are present in all the coatings and that when using tartaric acid, a relatively high level of amorphism is reached. The electrochemical and corrosion behaviours are evaluated by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) performed in a heated sulphuric acid solution. It is found that all types of coatings provide protection against corrosion, with oxides produced using glutamic acid showing the lowest corrosion current density (0.58 mA·m−2) and low corrosion rate (1.02 μm·y−1).

Acidic environments can cause serious corrosion problems on many metals, first of all carbon steel, widely employed industrially. The implementation of functional instruments for the prediction of the corrosion rate represents a powerful tool for the design and for an efficient management strategy of the plants. The Tafel-Piontelli model, introduced in 2017, is a mechanistic model developed for this purpose. Its theoretical foundations derive from one of the fundamental laws that characterize the kinetics of the corrosion process: the Tafel's law. The model can be easily applied to any metal with active behavior in contact with an acidic environment where hydrogen evolution is the dominant cathodic process. Its performance is tested by comparison with the experimental data obtained via mass loss tests. The results are promising: the model is in fact able to successfully predict not only the order of magnitude of the corrosion rate, but also its exponential trend with respect to temperature and pH.